The effectiveness of dry powders in extinguishing fires has been known for some time. Sodium bicarbonate, potassium bicarbonate, monophosphate, potassium chloride (Purple K) and potassium salt are some powders that have been used in fire extinction systems. Silicone may be added to the dry powder to aid in the powder's free flow. Even silicone alone has been used effectively as a dry powder to extinguish fires.
A liquid, and more particularly, a liquid foam may be used in conjunction with a dry powder for extinguishing a fire. For the powder to operate effectively in this situation, however, it should be prevented from wetting. Further, if the powder is not well treated with an anti-wetting composition, the powder may break down the foam.
It is known in the art to coat the dry chemicals used as powders to fight fires with silicone or other anti-wetting compositions. It is recommended, in the applications discussed herein, to use "foam compatible" powders as defined by the NFPA. Experience indicates that treated powders can comingle with foam at the site of the fire without inhibiting either product's fire extinguishing properties.
The use of dry powder to extinguish fires has at least two significant disadvantages. Dry powder is difficult to spray for any distance. Thus, the spraying nozzle for dry powder alone must be drawn much closer to the fire than a liquid nozzle. Further, a fire extinguished by powder has a definite propensity to reignite under common circumstances. If a three dimensional fire, in particular, has burned long enough to heat elements in its environment, such as metals, although the dry powder may extinguish the fire, it is likely to reignite when the powder dissipates.
The term two dimensional (or static) fire is used herein to indicate the combustion of a non-replenishing fluid or solid. An example of a two dimensional fire is the burning of a tank or pond that is not, or at least is no longer, being fed from a remote source. The term three dimensional (or dynamic) fire, by distinction, is used to refer to a fire that is fed by a remote replenisbing source. A well blow out and a burning tanker (the burn area being fed by fluid from within) are examples of three dimensional, dynamic fires.
Dry powder is particularly useful in extinguishing a three dimensional fire, subject to the above disadvantages. Liquids and liquid foam mixtures are particularly useful in extinguishing static, two dimensional fires, as well as in cooling and reducing the size of three dimensional fires. It is quite difficult, however, with liquid and liquid foam mixtures alone, to extinguish a three dimensional fire.
The alternating use of powders and liquids on fires has been attempted. The difficulty with this technique is the degree of coordination required and the close approach to the fire required for the powder nozzle.
The present invention discloses a method and apparatus for applying simultaneously dry powder and liquid, including a liquid foam mixture, to a fire. The method and apparatus is particularly useful for the extinction of three dimensional fires, together with their associated static fires. The method and apparatus achieves not only the advantage of permanently extinguishing a three dimensional fire but also the enhanced safety of permitting operation from a greater distance by extending the distance over which dry powder can be effectively sprayed.
The invention further discloses method and apparatus for adjusting the velocity of the powder stream in order to coordinate that velocity with the distance from the fire of the applying mechanism, be it hand held nozzle or monitor. The ability to adjust the velocity of the powder to coordinate with the distance from the fire of the applying mechanism helps to ensure that the powder stream terminates at the fire, rather than shooting through it.
It has been found that use of the present invention has the further advantage that the amount of dry chemical or powder required to extinguish a fire can be reduced drastically, from say 500 pounds to 75 pounds.